Thursday 7 August 2014

A small Sprassodont Mammal from the Middle Miocene of southern Bolivia.

South America was effectively an island continent for much of the Cenozoic, connected only to Antarctica in the south. As such it was not colonized by carnivorous Placental Mammals until the closure of the Panama Seaway at the end of the Miocene. Instead it developed a unique set of carnivores of its own, including Phorusrhacid ‘Terror Birds’, giant Boine and Madtsoiid Snakes, Sebecosuchian Crocodyliformes, Didelphoid Marsupials and the Sprassodonts, a groups of carnivorous Metatheran Mammals related to Marsupials, but which diverged from them before the last common ancestor of all living Marsupials (Australian and South American).

In a paper published in the Journal of Vertebrate Paleontology on 6 May 2014, Russell Engleman of the Department of Biology at Case Western Reserve University and Darin Croft of the Department of Anatomy at the Case Western Reserve University School of Medicine describe the skull of a small Sprassodont Mammal from Quebrada Honda in the Tarija Department of Bolivia. 

The specimen clearly represents a new species, however it consists only of a single, somewhat crushed, skull, so Engleman and Croft have refrained from formally naming it, in the hope that more material will become available in future, enabling a better description of the species, and instead refer to it by its specimen number, UF 27881. 

UF 27881 is a 3 cm Sprassodont Mammal skull with a shortened snout. The braincase and snout are crushed and poorly preserved, the preservation of the palate is good, but most of the teeth are missing.

Dorsal views of the crania of UF 27881. (A) photograph, (B) line drawing and  (C) reconstruction. Abbreviations: fr, frontal; iof, infraorbital foramen; lac, lacrimal; lat, lacrimal tubercle; mjs, maxillojugal suture; mx, maxilla; na, nasal; opl, orbital platform; tl, temporal line. Scale bar is 3 cm. Engleman & Croft (2014).

Its small size makes UF 27881 one of the smallest known Sprassodont Mammals, and Engleman and Croft suggest that this, combined with its general skull morphology, make it likely that it was an ambush predator with a hunting strategy similar to that of Martens, Quolls and some Cats, capable of taking relatively large prey items (compared to itself).

Ventral view of the crania of UF 27881. (A) photograph and (B) line drawing. Abbreviations: iof, infraorbital foramen; mch, ‘cheek’ of maxilla (sensu Forasiepi, 2009); mpf, major palatine foramen; mx, maxilla; pa, palatine; pp, palatal pit; uaf, unnamed anterior foramen. Scale Bar is 3 cm. Croft & Engleman (2014).

See also…

Thylacinids (Thylacinidae) were large carnivorous Australian...

The Hyaenodontidae were a group of carnivorous Mammals the appeared in the the Late Palaeocene and continued till the Late Miocene. Their name means 'Hyena-toothed', though they are not closely related to the Hyenas, or any other extant Mammal group. They were formerly classified with the Oxyaenids in a group called the Creodonts, though that group is now thought to be polyphyletic; i.e. the two groups which formerly were classified together to form the Creodonts are no longer thought to be closely related.

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